Dual-Source Mirau Interferometry for On-Machine Surface Metrology
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Solution Overview
Problem
Existing interferometric systems for measuring surface characteristics are costly, complex, and unsuitable for on-machine metrology due to their large size, requiring multiple instruments for comprehensive evaluation, and traditional methods like phase-shifting interferometry are time-consuming and sensitive to environmental disturbances.
Innovation Solution
A dual-mode interferometric system using two light sources (laser and LED) with a Mirau type microscope configuration and a deep learning algorithm to process two interferograms, enabling simultaneous measurement of surface shape and roughness without mechanical vibrations, ambient air turbulence sensitivity, and reducing the need for multiple instruments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional interferometric systems are used to measure surface characteristics, then measurement accuracy is improved, but device complexity and cost increase
Solution Approach 1:
The patent combines multiple measurement functions (surface shape measurement and surface roughness measurement) into a single interferometric system. The system integrates two light sources (laser and LED) and uses a unified optical path with a Mirau objective to achieve both measurement types simultaneously, eliminating the need for separate instruments and reducing overall system complexity.
Solution Approach 2:
The interferometric system is designed with multi-functionality to perform both surface shape measurement (using laser light) and surface roughness measurement (using LED light) through the same optical apparatus. This universal design allows a single system to replace multiple specialized instruments, reducing device complexity while maintaining measurement precision.
2Measurement precision
If phase-shifting interferometry is used to measure surface characteristics, then measurement accuracy is improved, but measurement time increases
Solution Approach 1:
The system employs periodic phase shifting through a piezoelectric actuator that modulates the reference mirror position. By using periodic phase shifts with specific frequencies, the system can capture multiple interferograms in rapid succession, enabling real-time surface measurement while maintaining high accuracy through the periodic sampling of phase information.
Solution Approach 2:
The patent replaces traditional mechanical phase-shifting mechanisms with a piezoelectric actuator that provides faster, more precise control. This substitution reduces mechanical inertia and measurement time while maintaining the ability to perform accurate phase-shifting interferometry for surface characterization.
3Measurement precision
If traditional interferometric systems are used for surface measurement, then measurement accuracy is improved, but sensitivity to environmental disturbances increases
Solution Approach 1:
The system uses a beam splitter and Mirau objective configuration that creates a compact measurement path, reducing the optical path length exposed to environmental disturbances. The beam splitter divides the light path into reference and measurement arms, allowing for differential measurement that compensates for environmental noise while maintaining high measurement accuracy.
Solution Approach 2:
The system utilizes two different light sources with distinct wavelengths (laser and LED) to perform measurements. By changing the wavelength parameter, the system can optimize measurements for different surface characteristics and reduce sensitivity to specific environmental disturbances that may affect particular wavelengths differently, thereby maintaining measurement accuracy in varying environmental conditions.
4Adaptability or versatility
If multiple instruments are used for comprehensive surface evaluation, then measurement capability is improved, but device complexity increases
Solution Approach 1:
The patent merges surface shape measurement and surface roughness measurement capabilities into a single interferometric system. By integrating two light sources and using a unified optical path with a Mirau objective, the system achieves comprehensive surface evaluation without requiring multiple separate instruments, thereby reducing device complexity while maintaining versatile measurement capability.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate, real-time, and cost-effective on-machine measurement of surface shape and roughness with reduced complexity and environmental insensitivity, improving precision and efficiency in optical metrology.
Implementation Method 1
a collimator positioned to receive light from a first light source having a first wavelength or first range of wavelengths, and from a second light source having light with a smaller coherence length than light from the first light source
Implementation Method 2
a beamsplitter, and a Mirau type microscope configuration including an objective lens, a plate with a central reflective spot and a beamsplitter plate to produce a reference beam and a test beam for illuminating the object
Implementation Method 3
an imaging lens positioned to receive the test beam and the reference beam; light from the test and reference beams upon reaching an image plane of the imaging lens form a plurality of interferograms at the image plane
Data Source
AI summary
Methods, devices and systems for measuring surface roughness and surface shape of an object are described. An example interferometric system includes a collimator and a first and a second light sources with different spectral ranges and different coherence lengths. The system selectively allows light from one of the light sources to reach the collimator, and also includes a beamsplitter, and a Mirau type microscope having an objective lens, a plate with a central reflective spot and a beamsplitter plate to produce a reference beam and a test beam. An imaging lens receives the test and reference beams that form a plurality of interferograms. A neural network receives two of the interferograms for measuring the surface shape and another two interferograms for measuring the surface roughness of the object. The interferometric systems have a compact form, making them suitable for on-machine measurements and other applications.